docs: Clarify FUSE configuration guidance

The FUSE reference mentioned an unshipped backend and repeated settings behavior in the environment-file reference. Remove the backend mention and keep settings behavior in the settings reference, with a link from the environment option.

content/manuals/ai/sandboxes/configuration/environment-files.md

@@ -688,11 +688,9 @@ store. Set it to `off` to omit the mount, `readonly` to mount the store read-onl
 or `readwrite` to let the sandbox modify shared skills. If omitted, it uses the
 daemon's default, which is `readonly` unless your organization overrides it.
 
-`fuse` inherits the [`sandbox.fuse`](settings.md#sandboxfuse) setting when
-omitted. Set it to `false` to disable FUSE access for this sandbox. Setting it
-to `true` cannot override `sandbox.fuse: false`. The option applies when the
-sandbox is created; existing sandboxes retain their configuration. The
-experimental Runtime backend and cloud sandboxes reject `fuse: true`.
+Set `fuse` to `false` to disable FUSE access for this sandbox. See the
+[`sandbox.fuse` setting](settings.md#sandboxfuse) for defaults and when changes
+take effect.
 
 ### `lifecycle`
 

content/manuals/ai/sandboxes/configuration/settings.md

@@ -213,8 +213,8 @@ $ sbx settings set sandbox.fuse false
 Changes apply only to newly created sandboxes. Existing sandboxes retain their
 FUSE configuration, including after restarts. To disable access for one sandbox,
 set [`sandboxOptions.fuse`](environment-files.md#sandboxoptions) to `false`
-in its environment file. FUSE is unsupported by the experimental Runtime
-backend and cloud sandboxes.
+in its environment file. When this setting is `false`, environment files cannot
+enable FUSE access. Cloud sandboxes do not support FUSE.
 
 #### ssh.agentForwardingEnabled {.wrap-anywhere}